摘要:Hyperledger Fabric is a distributed operating system for permissioned blockchains hosted by the Linux Foundation. It is the first truly extensible blockchain system for running distributed applications at enterprise grade scale. To achieve this, Hyperledger Fabric introduces a novel execute-order- validate blockchain architecture, allowing parallelization of transaction execution and validation. However, this raises the need for transaction isolation. Today transaction isolation is attained by locking the entire state database during simulation of transactions and database updates. This lock is one of the major performance bottlenecks as observed by previous work. This work presents a new lock-free approach for providing transaction isolation. It harnesses the already existing version- ing of key-value pairs in the database, used primarily for a read-write conflict detection during the validation phase, to create a version-based snapshot isolation. We further im- plement and evaluate our new approach. We show that our solution outperforms the current implementation by 8.1x and that it is comparable to the optimal solution where no isolation mechanism is applied.

摘要:Blockchain is well known as a decentralized and distributed public digital ledger, and is currently used by most cryptocurrencies to record transactions. One of the fundamental differences between blockchain and traditional distributed systems is that blockchain’s de- centralization relies on consensus protocols, such as proof of work (PoW). However, com- putation systems, such as application specific integrated circuit (ASIC) machines, have re- cently emerged that are specifically designed for PoW computation and may compromise a decentralized system within a short amount of time. These computationally resource- ful miners challenge the very nature of blockchain, with potentially serious consequences. Therefore, in this paper, we propose a general and flexible PoW method that enforces memory usage. Specifically, the proposed method blocks computationally resourceful min- ers and retains the previous design logic without requiring one to replace the original hash function. We also propose the notion of a memory intensive function (MIF) with a mem- ory usage parameter k ( k MIF ). Our scheme comprises three algorithms that construct a k MIF Hash by invoking any available hash function which is not k MIF to protect against ASICs, and then thwarts the pre-computation of hash results over a nonce. We then de- sign experiments to evaluate memory changes in these three algorithms, and the find- ings demonstrate that enforcing memory usage in a blockchain can be an effective defense against computationally resourceful miners.

摘要:Blockchain technologies are on the rise, and Hyper- ledger Fabric is one of the most popular permissioned blockchain platforms. In this paper, we re-architect the validation phase of Fabric based on our analysis from fine-grained breakdown of the validation phase’s latency. Our optimized validation phase uses a chaincode cache during validation of transactions, initiates state database reads in parallel with validation of transactions, and writes to the ledger and databases in parallel. Our experiments reveal performance improvements of 2×for CouchDB and 1.3× for LevelDB. Notably, our optimizations can be adopted in a future release of Hyperledger Fabric.

摘要:Bitcoin, as well as many of its successors, require the whole transaction record to be reliably acquired by all nodes to prevent double-spending. Recently, many blockchains have been proposed to achieve scale-out throughput by letting nodes only acquire a fraction of the whole transaction set. However, these schemes, e.g., sharding and off-chain techniques, suffer from a degradation in decentralization or the capacity of fault tolerance. In this paper, we show that the complete set of transactions is not a necessity for the prevention of double-spending if the properties of value transfers is fully explored. In other words, we show that a value-transfer ledger like Bitcoin has the potential to scale-out by its nature without sacrificing security or decentralization. Firstly, we give a formal definition for the value-transfer ledger and its distinct features from a generic database. Then, we introduce the blockchain structure with a shared main chain for consensus and an individual chain for each node for recording transactions. A locally executable validation scheme is proposed with uncompromising validity and consistency. A beneficial consequence of our design is that nodes will spontaneously try to reduce their transmission cost by only providing the transactions needed to show that their transactions are not double spend. As a result, the network is sharded as each node only acquires part of the transaction record and a scaleout throughput

摘要:Although the emergence of the programmable smart contract makes blockchain systems easily embrace a wider range of industrial areas, how to execute smart contracts efficiently becomes a big challenge nowadays. Due to the existence of Byzantine nodes, the mechanism of executing smart contracts is quite different from that in database systems, so that existing successful concurrency control protocols in database systems cannot be employed directly. Moreover, even though smart contract execution follows a two-phase style, i.e, the miner node executes a batch of smart contracts in the first phase and the validators replay them in the second phase, existing parallel solutions only focus on the optimization in the first phase, but not including the second phase. In this paper, we propose a novel efficient concurrency control scheme which is the first one to do optimization in both phases. Specifically, (i) in the first phase, we give a variant of OCC (Optimistic Concurrency Control) protocol based on batching feature to improve the concurrent execution efficiency for the miner and produce a schedule log with high parallelism for validators. Also, a graph partition algorithm is devised to divide the original schedule log into small pieces and further reduce the communication cost; and (ii) in the second phase, we give a deter- ministic OCC protocol to replay all smart contracts efficiently on multi-core validators where all cores can replay smart contracts independently. Theoretical analysis and extensive experimental results illustrate that the proposed scheme outperforms state-of- art solutions significantly.

摘要:A smart contract is an electronic transaction protocol intended to digitally facilitate, verify, or enforce the negotiation and execution of the terms of an underlying legal contract designed to fulfil common contractual conditions comprising payments, legal obligations, and enforcement without third parties. Thus, by following the traditional perception, smart contracts target to reduce transaction costs including arbitration and enforcement costs by realising trackable and irreversible transactions by using blockchain technology for distributed databases. However, the potential of smart contracts goes far beyond cost reductions by facilitating the entrepreneurial collaboration of cross-organisational businessprocesses that are characteristic for smart supply chains. A closer look to existing or ongoing smart contract projects reveals that the majority of smart-contract applications in business life are linked to supply chain management, Internet of Things and Industry 4.0 solutions. The author participated in several EU projects related to transnational entrepreneurial networks and smart supply chains. Thus, the paper discusses the research question of how and to which extent smart contracting and blockchain technology can facilitate the implementation of collaborative business structures for sustainable entrepreneurial activities in smart supply chains. The research is based on expert interviews, surveys and case studies, which took place in the context of the EU projects with a focus on the Baltic Sea Region.

摘要:Within the last few years, a countless number of blockchain systems have emerged on the market, each one claiming to revolutionize the way of distributed transaction processing in one way or the other. Many blockchain features, such as byzantine fault tolerance, are indeed valuable additions in modern environments. However, despite all the hype around the technology, many of the challenges that blockchain sys- tems have to face are fundamental transaction management problems. These are largely shared with traditional database systems, which have been around for decades already. These similarities become especially visible for systems, that blur the lines between blockchain systems and classical database systems. A great example of this is Hyperledger Fabric, an open-source permissioned blockchain system un- der development by IBM. By implementing parallel trans- action processing, Fabric’s workfow is highly motivated by optimistic concurrency control mechanisms in classical database systems. This raises two questions: (1) Which con- ceptual similarities and diferences do actually exist between a system such as Fabric and a classical distributed database system? (2) Is it possible to improve on the performance of Fabric by transitioning technology from the database world to blockchains and thus blurring the lines between these two types of systems even further? To tackle these questions, we frst explore Fabric from the perspective of database research, where we observe weaknesses in the transaction pipeline. We then solve these issues by transitioning well-understood database concepts to Fabric, namely transaction reordering as well as early transaction abort. Our experimental eval- uation under the Smallbank benchmark as well as under a custom workload shows that our improved version Fabric++ signifcantly increases the throughput of successful transac- tions over the vanilla version by up to a factor of 12x, while decreasing the average latency to almost half.

摘要:TheriseofsmartcontractsystemssuchasEthereum has resulted in a proliferation of blockchain-based decentralized applications including applications that store and manage a wide range of data. Current smart contracts are designed to be executed solely by miners and are revealed entirely on-chain, resulting in reduced scalability and privacy. In this paper, we discuss that scalability and privacy of smart contracts can be enhanced by splitting a given contract into an off-chain contract and an on-chain contract. Specifically, functions of the contract that involve high-cost computation or sensitive information can be split and included as the off-chain contract, that is signed and executed by only the interested participants. The proposed approach allows the participants to reach unanimous agreement off-chain when all of them are honest, allowing computing resources of miners to be saved and content of the off-chain contract to be hidden from the public. In case of a dispute caused by any dishonest participants, a signed copy of the offchain contract can be revealed so that a verified instance can be created to make miners enforce the true execution result. Thus, honest participants have the ability to redress and penalize any fraudulent or dishonest behavior, which incentivizes all participants to honestly follow the agreed off-chain contract. We discuss techniques for splitting a contract into a pair of on/off-chain contracts and propose a mechanism to address the challenges of handling dishonest participants in the system. Our implementation and evaluation of the proposed approach using an example smart contract demonstrate the effectiveness of the proposed approach in Ethereum.

摘要:比特币是中本聪（Nakamoto）于2008年提出的数字货币，它具有去中心化、跨国界和发行总量 固定等特性，现在已经成为使用最广泛的数字货币之一．然而，比特币设计初期的一些人为限制，导致现 有网络处理交易的速率十分有限，最近交易处理能力已经接近上限，交易确认时间显著增加．这不仅严 重影响比特币的使用体验，进而限制使用范围，而且对比特币的设计提出更高的要求．针对比特币所面 临的交易处理性能挑战，以提升区块链容量为目标对比特币展开深入研究．首先，分析比特币当前网络 状态，根据比特币交易数据，统计交易延迟情况；其次，针对链上扩容方案，分析可行性，研究扩容效果；再次，针对链下扩容方案，分析作用原理，研究扩容效果；最后，分析链上／链下扩容方案优缺点，提出适 应社区的可行的比特币扩容路线方案．最新比特币扩容的进展进一步证明了我们结论的正确性。

摘要:Blockchain is very important in finance field and electronic business field, so many researchers are attracted to study the technologies of blockchain. Since the transactions in blockchain takes much time, and they make the blockchain poor efficiency, business processes across organizations require the transactions as soon as possible. Concurrency is attracted much attention and is very important in blockchain field. In this paper, a novel decentralized blockchain network model with high concurrency is proposed. First, the idea of the proposed model is stated. Second, the high concurrency blockchain network model is proposed. Third, the corresponding algorithms are designed according to the proposed model. Furthermore, the experiment is conduced and the results show that proposed model works well.

摘要:区块链是一种结合分布式共识、加密、时间戳等方法,在不依赖任何第三方中心化机构的情况下,实现点 对点交易、协调以及协作的技术.近几年,区块链技术的不断发展引起了产业界和学术界的极大兴趣.但是,区块链的 存储可扩展性问题,提高了区块链设备的门槛,成为了区块链应用落地的瓶颈.介绍了区块链的基本原理和存储模 型,分析了当前区块链所面临的存储问题;然后,针对区块链存储可扩展性问题,从链下存储和链上存储这两条技术 路线出发,论述了主要的解决方案的原理与思路;最后,总结了提高区块链存储可扩展性的技术研究进展,指出了当 前解决方案所面临的问题,为未来的研究工作提供了方向.

摘要:Modern cryptocurrency systems, such as Ethereum, permit complex financial transactions through scripts called smart contracts. These smart contracts are executed many, many times, always without real concurrency. First, all smart contracts are serially executed by miners before appending them to the blockchain. Later, those contracts are serially re-executed by validators to verify that the smart contracts were executed correctly by miners. Serial execution limits system throughput and fails to exploit to- day’s concurrent multicore and cluster architectures. Nevertheless, serial execution appears to be required: contracts share state, and contract programming languages have a serial semantics. This paper presents a novel way to permit miners and validators to execute smart contracts in parallel, based on techniques adapted from software transactional memory. Miners execute smart con- tracts speculatively in parallel, allowing non-conflicting contracts to proceed concurrently, and “discovering” a serializable concurrent schedule for a block’s transactions, This schedule is captured and encoded as a deterministic fork-join program used by validators to re-execute the miner’s parallel schedule deterministically but concurrently. Smart contract benchmarks run on a JVM with ScalaSTM show that a speedup of 1.33x can be obtained for miners and 1.69x for validators with just three concurrent threads.

摘要:摘要:现有区块链主要分为公链和联盟链，公链是区块链思想的本源，然而现有公链体系存在匿名 账户难以与现实世界对应，以及系统执行效率低两大缺陷，同时，联盟链较差的隐私性和信息安全性又备 受诟病，鉴于此，提出许可公链(permissionedpublicblockchain,PPC)的概念和实现方案.许可公链通过链 ，上分布式密码学注册方案，实现公共许可机制;通过可订阅二层合约、区块快速转发和结构化广播3个技 术提高大规模区块链的交易速度，因此，许可公链融合联盟链的许可机制与公链技术，是面向公众用户的、 可监管的创新公链方案、所提出许可公链系统不仅建立个人和账户的安全隐私对应关系，而且新架构灵活 高效，可支持复杂的实际应用，尤其适用于金融业务与智能金融监管。

摘要:以上海证券交易所“去中心化的主板核心交易系统”作为业务场景,旨在研究高性能联盟区块链的优化算 法.在联盟链关键技术研究的基础上,结合现有主板证券竞价交易系统的业务,提出了系统架构以及关键技术的实 现.对业务逻辑与共识分离、存储优化和数字签名验证优化(包括合并验签和 GPU 加速)等可提高联盟链性能的优 化策略进行了详细的介绍和分析.最后,通过一系列对比实验来验证优化策略的有效性.实验结果表明,这些优化手 段极大地提高了去中心化的主板核心交易系统的性能.

摘要:Blockchain-based platforms, such as Ethereum, allow trans- actions in blocks to call user-defined scripts named smart contracts. In the blockchain network, after being generated by a miner, a block will be validated many times by the peers who accept it. Hence by enabling concurrency on smart contracts, especially validation, we can improve the efficiency and the throughput of those platforms. By introducing multiversion transaction ordering, this paper presents a concurrent scheme called MVTO to run smart contracts concurrently. First, the miners are able to use any concurrency control technique to discover a conflict-serializable schedule. Then, validators use MVTO to verify the block by replaying this schedule concurrently and deterministi- cally. The evaluation shows that this mechanism achieves approximately 2.5x speedup in the block validation using a thread pool with 3 threads.